The present invention relates to a device for generating a signal that forms a representation of the position of incidence of a beam of radiation onto an elongate detector forming part of the device.
Such detectors are much used in the field of land surveying, and particularly as altimeter. Use is made here of a laser light source which emits a bundle of laser light propagating in hoizontal direction. In general this laser light source is embodied such that the laser light beam emitted thereby rotates in the horizontal plane. To this end the laser light source is generally provided with a rotatably driven prism arranged on top of the laser light source which reflects the laser beam radiated upward from the laser light source into the horizontal plane. Such a configuration is otherwise shown in FIG. 1.
Such detectors are also used in laser measuring systems wherein the laser beams extend at least partially vertically.
At some distance herefrom, whereby distances in the order of magnitude of several tens to several hundreds of meters should be envisioned, a laser receiver is located which delivers an output signal representing the height at which the laser beam emitted by the laser light source strikes the laser receiver. For this purpose such a laser receiver is provided with a detector.
In accordance with a known type of laser receiver, such a detector is formed by a number of detector elements which, when such a detector element is struck by a laser beam, each generate a signal. This signal is generally fed to a digital processing circuit, wherein the processing circuit generates a digital output signal that forms a representation of the height at which the laser beam strikes the laser receiver.
Also known are laser receivers in which is used a laser detector of limited dimensions which is movable in vertical direction along the laser receiver. Such laser receivers are controlled such that the detector "searches" as it were for the laser bundle and follows it when there are changes of height. These laser receivers embodied with mechanically moving parts have the drawback that they are comparatively slow, so that when there are rapid changes in the height of the received laser bundle the output signal cannot follow these rapid changes, and these are therefore less suitable for controlling fast-working apparatus.
It should be borne in mind here that the output signal of such receivers can be used for instance for controlling cutting apparatus for cutting away road surfaces, grinding apparatus for grinding grooves in road surfaces, and for instance for ballast bed packing machines for tamping ballast under railway sleepers so that the railway tracks assume the correct height.
Such laser receivers otherwise have the drawback that they are also sensitive to light originating from the same laser transmitter and which has been reflected by random objects. The thus reflected laser beams can have a disadvantageous effect on the proper operation of the detector, so that the output signal is not an exact indication of the position of incidence of the laser beam. The same is true of the first mentioned type of detector.